1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor thin film, and methods of manufacturing an electronic device and a liquid crystal display device, and more particularly relates to a method of manufacturing a crystalline semiconductor thin film, and methods of manufacturing an electronic device and a liquid crystal display device constituted by the semiconductor thin films manufactured by the foregoing method.
2. Description of the Related Art
Japanese Patent publication No. 2004-119,518 (called “Reference 1”) discloses a method of manufacturing a crystalline semiconductor thin film assuring high carrier mobility. In the method, an amorphous semiconductor thin film is deposited on an insulating substrate. Energy beams are illuminated onto the amorphous semiconductor thin film in order to change amorphous properties to crystal properties, so that a crystalline semiconductor thin film will be formed. Specifically, the amorphous semiconductor thin film is fused by energy beams, is solidified, and is changed into the crystalline semiconductor thin film.
The foregoing method is applied to manufacturing a thin film transistor (TFT) of a liquid crystal display device (liquid crystal display panel). Specifically, an amorphous Si (silicon) thin film is formed on a transparent quartz substrate via an insulating layer. Laser beams are illuminated onto the amorphous silicon (Si) thin film, which is changed to a polycrystalline Si thin film. The polycrystalline Si thin film is used as a source region, a channel forming region or a drain region of a thin film transistor.
When energy beams are illuminated onto the amorphous Si film placed on the flat transparent quartz substrate, heat generated by the energy beams is uniformly conducted into the quartz substrate. Therefore, it is impossible to control, in the quartz substrate, positions of crystal producing nucleuses, and a speed at which the amorphous Si thin film is solidified. In short, it is impossible to control positions and diameters of Si crystal grains in the crystallized Si thin film.
In the liquid crystal display device, positions of and quantities Si crystal gains are different in source regions, channel forming regions and drain regions of each thin film transistor. This will lead to variations in electric properties such as carrier mobility, threshold voltages, and leak currents. Further, positions, quantity and diameters of Si crystal gains are different in respective source regions, channel forming regions and drain regions of each thin film transistor in each production lot. This also may lead to variations in the electric properties such as carrier mobility values, threshold voltages, and leak currents. The variations of electric properties will adversely affect performance of the liquid crystal display device.
When energy beams are illuminated onto the amorphous Si thin film, a crystalline Si thin film should be made in order to suppress the generation of irregular crystal nucleuses, to promote the generation and growth of crystal nucleuses at predetermined positions, and to have large crystal grains. Japanese Patent No. 3,464,287 (called “Reference 2”) describes the method, in which a metal element promoting crystallization is selectively introduced into an amorphous thin film in order to enable a crystalline thin film to be produced at a low temperature. Specifically, a masking material such as an aluminum nitride film is deposited on the amorphous thin film, and a partially porous mask is prepared by the photolithography or the like. Thereafter, a solution containing a metal element is selectively applied onto the amorphous thin film via the pores on the mask. The metal element partially crystallizes the amorphous thin film.
However, the following matters seem to remain unsolved in the crystalline thin film manufacturing method of Reference 2. Specifically, the mask for selectively applying the solution including the metal element has to be made through a plurality of manufacturing processes such as deposition of the masking material, application of a photo-resist film, making, exposure and development of a photo mask, and patterning (etching) of the masking material using the photo mask. This will lead to increases of the manufacturing processes and manufacturing cost, and lowering of a productivity rate and yield.